Printed sheets containing concealed images and method &amp; materials for preparation and visual development of same

ABSTRACT

A system for the preparing of copy containing concealed images and a marking material for the development of same in which the components comprise a receiving material in the form of starch or polyvinyl alcohol, an iodide which is oxidizable to iodine, and an oxidizing agent for oxidizing the iodide in which the oxidizing agent is contained in the imaging material to produce the concealed image, the iodine is contained in the marking material for the development of the image and the starch or polyvinyl alcohol are contained in the copy sheet, the printing material or the marking material whereby, when the marking material is applied to the concealed image, the oxidizing agent oxidizes the iodide to release iodine for producing an intense color with the starch or polyvinyl alcohol and in which the printing process is adapted to conventional printing systems.

United States Patent PRINTED SHEETS CONTAINING CONCEALED IMAGES ANDMETHOD & MATERIALS FOR PREPARATION AND VISUAL DEVELOPMENT OF SAME 11Claims, 3 Drawing Figs.

US. Cl l17/1.7, 35/9 R, 101/426,101/469, 10i/D1G. 1,106/21, 1l7/36.2Int. Cl 844i 1/10, B4lm 5/12, G09b 3/06 FieldofSearch l17/1.7, 36.2,36.7; 35/9; 101/426, 469, 470, DIG. 1; 106/21 Primary ExaminerWilliam D.Martin Assistant Examiner-Edward .I. Cabic Attorney-McDougall, Hersh,Scott & Ladd ABSTRACT: A system for the preparing of copy containingconcealed images and a marking material for the development of same inwhich the components comprise a receiving material in the form of starchor polyvinyl alcohol, an iodide which is oxidizable to iodine, and anoxidizing agent for oxidizing the iodide in which the oxidizing agent iscontained in the imaging material to produce the concealed image, theiodine is contained in the marking material for the development of theimage and the starch or polyvinyl alcohol are contained in the copysheet, the printing material or the marking material whereby, when themarking material is applied to the concealed image, the oxidizing agentoxidizes the iodide to release iodine for producing an intense colorwith the starch or polyvinyl alcohol and in which the printing processis adapted to conventional printing systems.

PRINTED SHEETS CONTAINING CONCEALED IMAGES AND METHOD & MATERIALS FORPREPARATION AND VISUAL DEVELOPMENT OF SAME This invention relates tomaterials, elements and methods used in informational systems andtesting systems embodying concealed or the combination of concealed andvisible images and in the preparation and development thereof.

A system of the type described finds utilization in the field that isreferred to as concealed image development where use is made thereof inself-instructional material, self-examination and multiple-choicetechniques for learning, testing and the like. In self-instructionalmaterial, only the image corresponding to the correct answer containsone or more components for visual development when properly marked witha writing substance embodying an additional component or componentsrequired for color development to indicate when the correct answer hasbeen marked.

In self-examination and in multiple-choice systems, the same conceptsare embodied. For further utilization of these concepts in concealedimage development, reference can be made to the copending applicationSer. No. 574,743, filed Aug. 24, 1966 and entitled Spirit Duplicationwith Visible and Concealed Images, now US. Pat. No. 3,451,143.

It is an object of this invention to provide a three-component systemfor use in the preparation and development of concealed images and it isa related object to provide materials and elements for use in thepractice of same, which give wider latitude in the distribution ofcomponents and in the utilization thereof in learning or instructionalsystems, which gives more rapid visible image development and increasedcolor intensity in the developed image, and which provides elementshaving greater shelf life and stability under widely varying conditionsof heat and humidity, and which are capable of use in conventionalprinting processes for preparation of multiple copies containing theconcealed image alone or in combinations with visible images.

These and other objects and advantages of this invention willhereinafter appear and for purposes of illustration, but not oflimitation, an embodiment of the invention is shown in the accompanyingdrawing in which FIG. 1 is a sectional elevational view showing thearrangement of elements in the imaging of a spirit master;

FIG. 2 is a schematic view, partially in section, of the imaged master;and

FIG. 3 is a schematic view, partially in section, showing the productionof printed copies from the imaged spirit master of FIG. 2.

The three-component system of this invention comprises an iodide capableof oxidation to release iodine, an oxidizing agent capable of oxidizingthe iodide to yield iodine, and a receiving material which reacts withthe released iodine to form an intensely colored product.

The invention will be described with reference to the distribution ofthe three components of the system in the elements of a spiritduplicating copy process for the production of multiple copiescontaining a concealed image for subsequent development and a markingmaterial with which the copy sheets can be marked for visibledevelopment of the image. It will be understood that the threecomponents can be otherwise distributed in elements for producingmultiple copies by other printing processes, such as stencilduplication, lithographic printing, letterpress printing, flexographicprinting, gravure printing, screen printing and the like, or by handstamp, as will hereinafter be defined.

As the iodide, it is preferred to make use of ammonium or an alkalimetal iodide, such as potassium iodide, sodium iodide and the like.Since the iodide is embodied in the marking material, use can be made ofcolored iodide salts capable of being oxidized to release iodine.

As the component with which the released iodine reacts to produce avisible image, use is made of a material that is invisible in the copysheet and, for such purpose, it is preferred to make use of a starch orpolyvinyl alcohol or mixtures thereof,

which is invisible when embodied in the desired amounts in the copysheet.

As the oxidizing agent, it is desirable to make use of material which isinvisible in the copy sheet to enable use in defining the invisibleimage. For this purpose, it is preferred to make use of a soluble saltof copper, such as the chloride, nitrate, sulphate, acetate, lactate,benzoate, or stearate of copper. Use can be made of a double salt CUCl'KCl and cupric ammonium chloride. Instead, use can be made of suchother oxidizing agents as copper-m-benzene disulfonate and the like.

Excellent results have been secured from the use of an invisibleoxidizing material referred to as positive halogen oxidizing agent inwhich the halogen is attached to nitrogen and which can be representedby trichloromelamine, N-chlorosuccinimide, N-bromosuccinimide,N-chlorophthalimide, monobromantin, diodantin, dibromomethyl ethylhydantoin, dichloro methyl ethyl hydantoin, N-bromoglutarimide, N-chloroglutarimide, N-haloaminotriazines, Dichloramine B" (WyandotteChemical Companys trademark for N,N- dichlorobenzenesulfonamide), andHalane" (Wyandotte Chemical Companys trademark forl,3-dichlor-5,5-dimethylhydantoin).

Copper chloride and related salts are highly hygroscopic or deliquescentsuch that difficulties are sometimes encountered in use underhigh-humidity conditions of the type prevailing in the southern regionsof the United States and on hot and humid summer days. The use of suchcopper salts can be greatly improved in their stability by thecombination with the copper salts of the type previously described.Excellent results are also secured by combination of the copper saltswith an amine such as piperidine, piperazine, phenylenediamine,tallowamine, trichloromelamine, triisopropanolamine, melamine, and thelike.

For the preparation of copy, in accordance with the preferred practiceof this invention, the oxidizing component is embodied in the transfercoating of the transfer sheet for use in imaging a spirit master. Thestarch or polyvinyl alcohol is embodied in the copy sheet. Since theiodide is subject to slow oxidation in air with corresponding release ofiodine and color it is undesirable to embody the iodide either in thecopy sheet or the printing material forming the invisible image appliedto the copy sheet. Thus the iodide is preferably embodied as a componentin the marking fluid with which the imaged copy sheet is marked todevelop the visible image when applied to engage the invisible image. Inanother ramification, the receiving material, such as starch and/orpolyvinyl alcohol, can be incorporated with the iodide in the markingmaterial.

Having described the basic concepts of this invention, illustration willnow be made by way of an example of the distribution of the elements inthe preparation of copy by spirit duplication and in the use thereof todevelop the invisible image.

EXAMPLE 1 Copy Paper In the preparation of the copy paper, it will besufficient if the copy paper is formulated to contain at least 0.1percent by weight starch and/or polyvinyl alcohol, although it ispreferred to make use thereof in an amount within the range of 0.5percent to 5 percent by weight of the copy paper. The starch orpolyvinyl alcohol can be incorporated for uniform distributionthroughout the copy paper by formulation as a component dissolved ordispersed in the slurry or finish of which the paper is formed byconventional papermaking technique. In the preferred practice, thestarch and/or polyvinyl alcohol is incorporated into already formedpaper by impregnation and preferably by coating the paper with asolution containing from 3-10 percent by weight starch or polyvinylalcohol in aqueous medium whereby the starch or polyvinyl alcohol isconcentrated on the surface of the paper where it is more available forreaction with the released iodine.

EXAMPLE 2 Transfer Sheet The transfer sheet embodying the oxidizingagent in the transfer coating can be prepared in the conventional mannerfor the preparation of transfer sheets in spirit duplication. Thefollowing is a typical formulation for a transfer coating in which theoxidizing material is incorporated:

8 pans by weight dioctyl phthalate 2.5 parts by weight ethyl cellulose40 parts by weight toluene EXAMPLE 2c 25 parts by Weighttrichloromelamine 8 parts by weight dioctyl phthalate 25 parts by weightethyl cellulose 40 parts by weight toluene EXAMPLE 2d parts by weightcopper-m-benzene disulfonate 15 parts by weight trichloromelamine 8 pansby weight dioctyl phthalate 2.5 parts by weight ethyl cellulose 40 partsby weight toluene The materials are ball milled and then coated ontopaper at the rate of 10 to pounds per 3,000 square feet of surface area,calculated on a dry weight basis.

As the oxidizing agent in examples 2 and 2b, the copper chloride can bereplaced by equivalent amounts of copper nitrate, copper sulphate,copper acetate, copper lactate, copper benzoate, copper-m-benzenedisulfonate, CuCl -Kcl with the copper salt being present preferably inan amount within the range of 5 to parts by weight. Instead of copperchloride, use can be made of cupric ammonium chloride. Instead of thetrichloromelamine in Example 2d, use can be made of other positivehalogen such as N-chlorosuccinimide, N-bromosuccinimide,N-chlorophthalimide, monobromantin, diodantin, dibromomethyl ethylhydantoin, dichloromethyl ethyl hydantoin, N-bromoglutarimide,N-chloroglutarimide, N-haloaminotriazines, Dichloramine B (WyandotteChemical Companys trademark for N,N-dichlorobenzenesulfonamide), andHalane" (Wyandotte Chemical Companys trademark forl,3-dichloro-5,S-dimethylhydantoin with the positive halogen beingpresent preferably in an amount within the range of 15 to parts byweight.

Instead of the oxidizing agent in examples 2 to 2d, use can be made of amixture of a copper salt and a positive halogen in the ratio of 1 partby weight copper salt to 0.2 to 2 parts by weight of the positivehalogen and preferably within the range of 1 part by weight of thecopper salt to 0.5 to 2 parts by weight of the positive halogen. Insteadof making use of a copper salt in example 2, use can be made of amixture of copper salts and an amine such as piperidine, piperazine,phenylenediamine, tallowamine, trichloromelamine, triisopropanolamine,melamine and the like, in the ratio of 1 part by weight copper salt toO.l to 2 parts by weight of the amine and preferably 1 part by weight ofthe copper salt to 0.4 to 2 parts by weight ofthe amine.

EXAMPLE 3 Marking Material The following is a typical formulation of afluid marking material:

The above fluid composition can be modified to embody a marking color,such as 0.0005 to 1 percent by weight of a dyestuff represented byCalcofast Spirit Yellow G. As the iodide, use can be made of potassiumiodide, sodium iodide, ammonium iodide, lithium iodide. The amount ofiodide is not critical since more or less can be used in the markingmaterial.

Instead of locating the marking iodide in a fluid system, it can beformulated into a wax crayon, pencil or the like element which can beused for marking.

EXAMPLE 4 Preparation of Copy by Spirit Duplication With reference nowto FIG. 1, the transfer sheet 2 is positioned with the transfer coating4 of example 2 in surface contact with the duplicating surface of aspirit master 6. The spirit master is imaged by transfer of coating fromthe transfer sheet to the master surface in the normal manner inresponse to impact or pressure from a die, typewriter key, stylus orpencil, or in response to a heat pattern generated by infrared radiationof an infrared ray absorbing original positioned in surface contact withthe transfer sheet. The master may be additionally imaged by aconventional spirit master to provide a master imaged in part with aspirit and alcohol soluble dyestuff from an imaged master having avisible image 8 and an invisible image 10.

For the production of copy, as illustrated in FIG. 2, the imaged master6 is mounted on the cylinder of a conventional spirit duplicationmachine and copy sheets 12, wetted on one surface 14 with a spiritfluid, are brought into surface contact with the imaged surface of themaster whereby some of the imaging materials are leached from the imagedportions of the master for transfer to the copy sheets to produce copiescontaining an invisible image 16 formed of the oxidizing agent andvisible images 18, if the master had an imaged portion containing adyestuff, or if the copy sheets originally contained a visible image.

Thereafter the copy sheets can be used as a piece of instructionalmaterial or test material distributed for use. When in marking the sheetwith the marking fluid of example 3, the marking fluid is applied to anonimaged portion of the sheet, only a color introduced by the markingmaterial to indicate the place that has been marked will show. When themarking material is applied to an invisible image, the iodide in themarking material is immediately oxidized by the oxidizing agent in theinvisible image to release iodine and the iodine stains or reacts withthe starch to provide a visible image of high color intensity toindicate that the marking material has been applied to a portion of thecopy sheet containing the visible image.

Having described the basic concepts of this invention, reference willnow be made to the distribution of components for use in other printingprocesses for producing multiple copies of the sheet printed with theinvisible and visible image.

In the lithographic printing process, the oxidizing material will befonnulated as a component of the lithographic ink which preferentiallywets the imaged portions of the lithographic surface as distinguishedfrom the nonimaged hydrophilic portions which are previously wet withwater.

In stencil duplication, the oxidizing agent is formulated in the stencilfluid that is forced through the stencil openings onto the copy sheetsto form the invisible image thereon.

In letterpress printing, the oxidizing material will be embodied in thefluid with which the letters of the plate are wet for imprinting thecopy sheets.

In gravure printing, the oxidizing material will be formulated into thefluid that is retained in the wells etched into the surface of the platefor transfer to copy paper brought into contact therewith.

In a hand stamp or in silk screen printing, the fluid ink would beformulated to contain the oxidizing agent.

In each of these other processes, the iodide would still be limited toformulation into the marking material with which the printed sheet ismarked and by polyvinyl alcohol or starch to be embodied with theoxidizing agent in the printing fluid or with the iodide in the markingmaterial and preferably in the paper on which the copy is produced.

The following example is typical of a printing ink embody- 0.25 gramAmmonium alum 9.00 grams Gum arabic 3.50 grams Penford Gum-Z00 075 gramFormalin L00 gram Sodium stearate 84.00 grams Water 36.5 grams Glycerine1000 ml. n-butanol 0.725 gram Trichloromelamine 0,725 gram CopperChloride The Penford Gum (starch) is heated and stirred until dissolvedor formed into a colloidal dispersion which is then combined with theremainder of the ingredients and dispersed as by means of a ball mill,colloid mill or the like.

The prepared ink composition can be applied to impression or copy paperwith a rubber stamp, a silk screen printing process, a jet printingprocess, or by letterpress. The dried ink images are invisible anddevelopment can be accomplished by treating the appropriate areas with a2 percent aqueous solution of potassium iodide,

In the above formulations, copper-m-benzene disulfonate can besubstituted for the trichloromelamine and either the trichloromelamineor copper chloride can be used solely as the oxidizing agent incorresponding amounts. Polyvinyl alcohol or carboxymethylcellulose canbe substituted for the Penford gum. The copper chloride ortrichloromelamine can be replaced with other copper salts or with apositive halogen oxidizing agent or combination thereof in amounts toconstitute 0.5 to percent by weight of the ink.

In the event that some slight color is present in the materials formingthe latent image, this can be concealed by the technique of making useof tinted copy or impression paper, preferably of the same tint as theimage so as better to conceal the image.

It will be apparent from the foregoing that we have provided a new andimproved system for use of concealed images in educational, testing andthe like programs whereby an invisible image can be made highly visiblewhen properly marked with an iodide-containing material.

It will be understood that changes may be made in the details ofconstruction, formulation and operation without departing from thespirit of the invention, especially as defined in the following claims.

We claim:

1. The method for imaging copy sheets with a concealed image and visualdevelopment of the concealed image comprising the steps of imaging acopy sheet with a printing material selected from the group consistingof a soluble copper salt and a positive halogen organic oxidizingcompound and mixtures thereof having no color value to provide aconcealed image and in which a receiving material selected from thegroup consisting of starch and polyvinyl alcohol and mixtures thereof isadmixed with the printing material or present as a component in the copysheet on which the printing material is applied, and subsequentlymarking the concealed image with a composition containing a solubleiodide which reacts with the material in the concealed image to releaseiodine which reacts with the receiving material for visual developmentof the concealed image.

2. The method as claimed in claim 1 in which the copper salt is selectedfrom the group consisting of the chloride, nitrate, sulphate, acetate,lactate, benzoate, or stearate of copper.

3. The method as claimed in claim 1 in which the positive halogencompound is selected from the group consisting of trichloromelamine,N-chlorosuccinimide, N-bromosuccinimide, N-chlorophthalimide,monobromantin, diodantin, dibromethyl ethyl hydantoin, dichloromethylethyl hydantoin, N-bromoglutarimide, N-chloroglutarimide and N-haloaminitriazines.

4. The method as claimed in claim I which includes with the copper saltor positive halogen compound and an amine selected from the groupconsisting of piperidine, piperazine, phenylenediamine, tallowamine,trichloromelamine, triisopropanolamine and melamine.

5. The method as claimed in claim 1 in which the iodide is selected fromthe group consisting of an alkali metal iodide and ammonium iodide.

6. The method as claimed in claim 1 in which the image is printed on thecopy sheet by a spirit duplicating process which makes use of a spiritmaster, a coated transfer sheet, copy sheets and a spirit fluid withwhich the copy sheets are wet before contact with the spirit master forleaching materials from the image for transfer from the master sheet tothe copy sheet, the copper salt or positive halogen compound is a spiritsoluble material contained in the transfer coating of the transfersheet.

7. The method as claimed in claim 6 in which the spirit master is alsoimaged with a conventional image containing a spirit soluble dye toprovide a master for producing a concealed image and a visible image onthe copy sheets.

8. The method as claimed in claim I in which, when the printing processis a stencil duplicating process, the copper salt or positive halogencompound is contained in the stencil fluid forced through the stencilopenings of a stencil sheet onto copy sheets to produce copy containingthe concealed image.

9. The method as claimed in claim 1 in which, when the printing processis a lithographic printing process, the copper salt or positive halogencompound is embodied in an oleophilic fluid with which the imagedlithographic plate is wet for transfer of the oleophilic fluid from theimaged areas of the master to copy sheets.

10. The method as claimed in claim 1 in which, when the printing processis a letterpress process, a gravure process, a silk screen printingprocess, a jet printing process, or a stamp process, the copper salt orpositive halogen compound is embodied in the printing ink.

11. A printed copy sheet comprising a visible image portion and aconcealed image portion containing a copper salt or positive halogencompound capable of oxidizing an iodide to iodine and in which theconcealed image portion contains a material selected from the groupconsisting of starch and polyvinyl alcohol which is responsive to thereleased iodine for the development of an intense color.

2. The method as claimed in claim 1 in which the copper salt is selectedfrom the group consisting of the chloride, nitrate, sulphate, acetate,lactate, benzoate, or stearate of copper.
 3. The method as claimed inclaim 1 in which the positive halogen compound is selected from thegroup consisting of trichloromelamine, N-chlorosuccinimide,N-bromosuccinimide, N-chlorophthalimide, monobromantin, diodantin,dibromethyl ethyl hydantoin, dichloromethyl ethyl hydantoin,N-bromoglutarimide, N-chloroglutarimide and N-haloaminitriazines.
 4. Themethod as claimed in claim 1 which includes with the copper salt orpositive halogen compound and an amine selected from the groupconsisting of piperidine, piperazine, phenylenediamine, tallowamine,trichloromelamine, triisopropanolamine and melamine.
 5. The method asclaimed in claim 1 in which the iodide is selected from the groupconsisting of an alkali metal iodide and ammonium iodide.
 6. The methodas claimed in claim 1 in which the image is printed on the copy sheet bya spirit duplicating process which makes use of a spirit master, acoated transfer sheet, copy sheets and a spirit fluid with which thecopy sheets are wet before contact with the spirit master for leachingmaterials from the image for transfer from the master sheet to the copysheet, the copper salt or positive halogen compound is a spirit solublematerial contained in the transfer coating of the transfer sheet.
 7. Themethod as claimed in claim 6 in which the spirit master is also imagedwith a conventional image containing a spirit soluble dye to provide amaster for producing a concealed image and a visible image on the copysheets.
 8. The method as claimed in claim 1 in which, when the printingprocess is a stencil duplicating process, the copper salt or positivehalogen compound is contained in the stencil fluid forced through thestencil openings of a stencil sheet onto copy sheets to produce copycontaining the concealed image.
 9. The method as claimed in claim 1 inwhich, when the printing process is a lithographic printing process, thecopper salt or positive halogen compound is embodied in an oleophilicfluid with which the imaged lithographic plate is wet for transfer ofthe oleophilic fluid from the imaged areas of the master to copy sheets.10. The method as claimed in claim 1 in which, when the printing processis a letterpress process, a gravure process, a silk screen printingprocess, a jet printing process, or a stamp process, the copper salt orpositive halogen compound is embodied in the printing ink.
 11. A printedcopy sheet comprising a Visible image portion and a concealed imageportion containing a copper salt or positive halogen compound capable ofoxidizing an iodide to iodine and in which the concealed image portioncontains a material selected from the group consisting of starch andpolyvinyl alcohol which is responsive to the released iodine for thedevelopment of an intense color.